In general, Celebrity still does mass market (or as they call it, premium) cruising better than the rest. But as of late, they have definitely slid in some areas, especially in terms of the ways in which they show customer appreciation and the way they run things on board.
For instance, there used to be a very discernible difference between Aqua Class and veranda/regular staterooms. I feel now there is virtually no distinction. You used to get a nice commemorative pin, an extra tote bag, daily water service and other "extras" that although token gestures, really made you feel special. These have all disappeared. For example, now instead of getting a special zippered tote bag along with a regular beach towel bag, you only get the zippered bag, and it's of extremely poor quality. In my group, 3 of our 4 bags broke within a day! No more daily water -- now they force you to go to a bar and order it, which is basically just a way to force people to buy the beverage packages.
Additionally, in terms of general downgrades in service, there is no more room service except for breakfast unless you want to pay a $5 delivery fee.